The present invention relates to star-block polymers and copolymers of monovinylaromatic compounds and conjugated dienes having functional groups associated with the nucleus of the copolymers.
Highly branched block copolymers, sometimes called star-block copolymers, are known in the art of anionic polymerization. These star-block copolymers are prepared by first forming linear block polymers having an active lithium atom on one end of the polymer chain. These active, linear polymer chains are then coupled by the addition of a polyfunctional compound having at least three reactive sites capable of reacting with the carbon to lithium bond on the polymer chains to add the polymer chain onto the functional groups of the compound. In the case where the polyfunctional compound is divinylbenzene, the coupling reaction results in a star-block having a cluster of living anionic species at the nucleus of the star. It is at this point that the reactive star anions are normally terminated by reaction with proton active reagents, such as alcohols, to yield the final polymer.
Zelinski, U.S. Pat. No. 3,280,084, polymerized butadiene with butyllithium initiator to form B-Li blocks (where B is polybutadiene) which when coupled with 0.02 to 1 part by weight per 100 parts of monomers of divinylbenzene gave star-block copolymers having polydivinylbenzene nuclei and several identical arms of polybutadiene branching therefrom. The arms can also be either random or block copolymers of styrene and butadiene (from A-B-Li blocks, where A is polystyrene segment) where the diene is the major component.
Farrar, U.S. Pat. No. 3,644,322, teaches to make star-block copolymers having several arms wherein half of the arms are grown out from the nucleus and then terminated with carbon dioxide or epoxides to form polar functional groups at the outer extremities of these arms.
Fletcher, U.S. Pat. No. 3,755,283, prepares hydroxyphenyl terminated star-block copolymers by using lithium p-lithiophenoxide as an initiator of linear chains, which chains are then coupled with polyfunctional coupling agents to form the star-block copolymers having the functional groups distant from the nucleus.
Milkovich et al, U.S. Pat. No. 3,786,116, teaches the end capping of linear block copolymers by reacting the carbon-to-lithium ends with various functional groups-producing termination agents. These agents, primarily produced by reacting halogen-containing compounds having a polymerizable moiety such as an olefinic group or an epoxy group, produced polymerizable block copolymers named macromonomers.
Fetters et al, U.S. Pat. No. 3,985,830, discloses a product having a nucleus of more than one molecule of m-divinylbenzene and at least three polymeric arms, each being a block copolymer of conjugated diene and monovinyl aromatic monomers wherein said conjugated diene block is linked to said nucleus.
Crossland et al, U.S. Pat. No. 4,010,226, teaches to form star-block copolymers using divinylbenzene as coupling agent, growing new arms from this star-blocked copolymers, which arms are 5000 to 1,000,000 molecular weight and then capping these longer arms at the extremities away from the nucleus wtih various reagents which react with the carbon-to-lithium bonds.
Tung et al, U.S. Pat. No. 4,169,115, teaches to form linear block copolymers which are then terminated by adding an episulfide. The terminated copolymer is then copolymerized with styrene by a free-radical initator to form block copolymers.
Bi et al, U.S. Pat. No. 4,180,530, teaches to form star-block copolymers having 60-95% by weight of a monovinyl aromatic compound and 5-40% by weight of a conjugated diene and having general formula (A--A'/B--B').sub.m X--B'--B/A').sub.n, where A is a block of vinyl aromatic compound, A'/B or B/A' is a block of random copolymer of the vinyl aromatic compound and the conjugated diene, B' is a block of conjugated diene monomer, m and n are integers whose sum is between 3 and 20, and X is the radical of a polyfunctional coupling agent forming the nucleus of the bimodal star-block copolymer.